Recording reproduction disks formed by applying magnetic sheet on both surfaces of the disk base have been known. In FIGS. 5-7, item 22 is a disk body comprised of a synthetic resin and glass filler the center of which has center hub receiving hole 22a, and annular recessed portions 22b were formed on both surfaces.
In order to accomplish the centering onto spindle 31 projected on turntable 30 in the disk drive for the disk main body 22, center hub 23 is attached to the inner circumference of one surface of the disk by adhesives or ultrasonic welding. The center hub has flange 24 on the outer circumference of one surface, and the center hole 25 is located at the middle. One surface 24a of flange 24 on the center hub 23 (the upper surface in FIG. 6) forms the disk datum placed on the before mentioned turntable 30, and the bottom surface 25a around the center hole 25 at the inner circumference of the flange 24 (the upper surface in FIG. 6) forms yoke plate application surface for yoke plate 10 to be held by the force of magnet 32 on the turntable. The yoke plate is made of a metal such as steel in a disc-form, and has tongue 11 on its outer circumference, and is attached to the outer side of yoke plate application surface 25a of the before mentioned center hub.
Magnetic sheet 20 is attached at or near the outer and inner diameters of the before mentioned disk main body 22. The recording reproduction disk 21 is comprised of disk main body 22, center hub 23, yoke plate 10, and a pair of magnetic sheets 20.
In known disks, disk datum 24a and yoke plate application surface 25a are formed on the center hub 23 which is fitted onto center hub hole 22a on the disk main body 22 with adhesives. The number of parts and adhesion processes required increases the complexity of assembly resulting in higher manufacturing cost. In addition, it has been necessary to provide sufficient adhesion to withstand the disk drive chucking force since the disk main body 22, and center hub 23, which is attached by an adhesive, are to be placed onto a turntable in the disk drive.